This invention relates generally to flow control and shutoff valves, and more specifically to butterfly valves.
Butterfly valves control the flow rate of a fluid by rotating a disc or plate within the fluid passage or bore. They are often selected because they are relatively simple to design, customize, and operate, and offer a wide flow control range. Different industries have developed specialized or unique features that are useful for different needs.
Many industries utilize sealing butterfly valves for many critical locations. In some cases, it is necessary to both regulate flow to an area, as well as to completely seal it off. Toward this end, certain valves include a butterfly disc with a sealing element proximate the outer circumference that fits tightly against the walls of the valve bore when the valve is closed, preventing fluid flow past the disc. Some valves may also include canted shafts to improve the sealing ability of the disc. However, these elements increase the force required to control the valve when approaching or leaving the closed position. Increased force can accelerate wear and frictional material loss in the valve, resulting in unseating of the butterfly disc from its position in the valve bore. Unseating of the disc can compromise flow control and lead to permanent binding of the disc or shaft in the bore resulting in valve failure.